Recently, in response to the requirement for high-quality imaging from the market, development of an electrophotographic toner suitable therefor has been promoted and there has been known, as such a toner, a polymerization toner which exhibits a narrow particle size distribution and enhanced reproducibility of minute dots and is produced by a process of emulsion polymerization and aggregation.
Meanwhile, to achieve energy saving, speed-up and space saving of an image forming apparatus, a toner with enhanced low-temperature fixability has been desired and to obtain such a toner, there is known a technique of lowering the melting point or fusion viscosity of a binder resin by use of a crystalline polyester resin. However, there were produced problems that such a toner resulted in lowering of mechanical strength (for example, stress resistance) or high-temperature off-set resistance.
As an invention to achieve both low temperature fixability and mechanical strength, for example, there was disclosed a polymerization toner comprised of multi-layered resin particles formed of layers of a crystalline polyester resin, a non-crystalline polyester resin and a crystalline polyester resin, as described in, for example, Patent document 1.
However, the foregoing polymerization toner produced problems that phenomena such as high-temperature offset.
To overcome such problems, there was proposed a toner comprised of a binder resin including a crystalline polyester resin, a non-crystalline polyester resin and an acryl resin having a cross-link structure (as described in, for example, Patent document 2). Such a toner, in which such an acryl resin having a cross-link structure acts as a high-elastic component, can achieve excellent high-temperature offset resistance, while maintaining low temperature fixability by the crystalline polyester resin.
However, the foregoing toner, in which the acryl resin having a cross-link structure was formed by use of a cross-linking agent of divinylbenzene, produced problems such that the achieved mechanical strength was low, that is, being fragile, resulting in image defects in the formed image.
Patent Document:
JP 2007-057823 A
JP 2010-055093 A